China must urgently invest more in updating sewage sludge treatment to avoid huge environmental costs in the future, a recently published analysis said.
The country is expected to produce 34 million metric tons of sewage sludge in 2015, an increase of 4 million tons from 2012.
“Historically, over 80% of the sludge has not been treated and disposed of effectively and safely,” researchers from the State Key Laboratory of Pollution Control and Resource Reuse at Tongji University wrote in their analysis.
Part the difficulty in efficiently disposing of the sludge is China’s practice of mixing municipal and industrial wastewater. By combining the two, heavy metals from industry such as Zinc, Chromium and Lead are introduced to the sludge, limiting disposal options.
In developed countries, sewage sludge is often used to help condition soil for farming. But introducing water laden with toxic metals into the soil could poison the land, making it unusable for farming.
China also combines municipal wastewater with rainwater, which introduces a disproportionate level of inorganic material, elminating treatment options such as composting, the paper said.
“The separate treatment of municipal wastewater, rainwater, and industrial wastewater should be considered to eliminate the problem of sewage sludge treatment and disposal,” the study, Dilemma of Sewage Sludge Treatment and Disposal in China, said.
“Even if this proposal were to be adopted, sludge treatment and disposal would remain a challenge.”
Alternative methods such as anaerobic digestion – introducing microorganisms to help break the waste down into methane and other biogases – have been funded and explored, but only a fraction of the facilities capable are in operation.
In 2013, there were 2600 sludge treatment centers. Of those, only 60 used anaerobic digestion and of those, only 10-30 were actually operational, “resulting in wasted infrastructure and treatment facilities”.
Part of the problem stems from funding. Much of the money towards treating waste goes to wastewater, which receives $68.8 billion annually versus the $5.6 billion going toward sewage sludge treatment.
“More investment in sludge treatment and disposal is urgently needed in China,” it said.
“If not, the investment in wastewater treatment could be in vain as the pollutants would re-enter the environment through sewage sludge.”
The opinion analysis was published Environmental Science and Technology on April 6.